In the grinding field, particularly for internal grinders for grinding bearing races, it is frequently encountered where a bearing race has a pair of oppositely disposed identical angle tapered bores, as in the cup of a double row tapered roller bearing. It is preferable that the bearing race have its tapered bores ground on a common setup, to insure concentricity with the support shoes, and squareness with the common drive plate of the machine. A single wheel of a wheel head is generally employed, which is movable in a radial direction of the workpiece to finish the bores. It is preferable that a constant dimension be held between identical gage diameters on the twin bores, to maintain the cone spacing in a final bearing assembly. The twin bores must therefore be ground in a precision manner, and would present no difficulty when turning the workpiece end-for-end and accomplishing the grind of each bore, except for the fact that the overall width of the workpiece may vary within given manufacturing tolerances from a standard gage master part. If a wider-than-standard workpiece were turned end-for-end and ground by a fixed grinding wheel movement, it is possible that deeper bores would be generated in opposite ends of the workpiece and the constant desired dimension would be decreased, thus allowing the cones of the final assembly to come closer together. It is therefore desirable practice to accomplish "gage grinding" of the bores; that is, wherein a gage finger is utilized to terminate the grind cycle at predetermined bore positions. One method that has been suggested is to use a single gage finger which may be applied internally to the first bore to be shaped and, thereafter, when the workpiece is turned end-for-end the gage finger would be axially advanced through the workpiece to recontact the then drive plate-facing bore to sense any shift of position which may be caused by the width tolerances of the workpiece. Thereafter, an iteration may be made to account for any location changes and the gage finger would be retracted out to the next to-be-ground bore to gage grind to a point insuring constancy of the gage dimension and subsequent spacing of the roller cones. One difficulty inherent in this scheme is that a complex gage head must be utilized with advancement means for shifting the gage finger back and forth axially within the workpiece. Additionally, location stops must be provided for the gage finger and thus inaccuracies may develop in the stopping points of the gage during its excursion through the workpiece.
Applicant has obviated the difficulties inherent in the prior art devices, by a unique gage grinding method utilizing a pair of gage fingers and selective sampling and comparing of previously ground diameters to known standards to accomplish a final grind of a tapered bore. One such grinder to which my invention may be adapted is defined in U.S. Pat. No. 3,157,007, which is an internal grinding machine having support shoes for radially supporting the workpiece and a drive plate for driving and axially supporting the workpiece while a grinding wheel is radially fed into the workpiece for a grinding operation. It is therefore the principle objective of this invention to maintain the standard spacing of two tapered bore gage diameters on a workpiece independent of workpiece length.